Wireless communication encoding and decoding techniques using variable length codes

ABSTRACT

A wireless communication encoding and decoding technique using variable length codes is disclosed. The coding technique defines the transmission time for a high bit in a continuous bit stream as (N×T) expressed in terms of time unit (T), and a low bit as (M×T). By assigning different transmission times to represent high and low bits in continuous bit streams, the total data transmission time can be reduced considerably in handling large amounts of digital data as compared with conventional coding techniques. Other advantages using this coding technique include power saving by the data communication device, which may be a battery-powered peripheral device or mobile unit, and more reliable signal synchronization at both ends of the communication link.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to wireless communication encodingand decoding techniques using variable length codes, in particular tosignal encoding and decoding techniques that assign differenttransmission times for high and low bits in the transmitted data,enabling considerable reduction in total transmission time and powersaving by the data communication device.

[0003] 2. Description of Related Arts

[0004] In wireless communication, data streams to be transmitted areencoded at the transmitting end, modulated into analogous waveform, andthen transmitted in the form of radio frequencies or infrared beams. Atthe receiving end, the analogous signals are received, amplified,demodulated to digital form, and then decoded to restore the originaldata format.

[0005] In wireless communication, the primary objective of variouscoding technique is to minimize the data transmission time, and maintainsignal synchronization at both ends to ensure reliable datatransmission.

[0006] The wireless communication encoding and decoding techniques notonly change the transmission time but also affect the power status ofthe data communication device. Commonly used wireless computerperipherals such as a keyboard and a mouse are connected by wirelessmeans to maintain bidirectional communication with the host computer.Since these devices are powered by a battery, the longer it takes totransmit a data stream, the battery operation hours of the transmittingdevice will be further decreased. Therefore, the choice of a signalcoding technique indirectly affects their power consumption and theoperation time of the device.

[0007] Generally, data are transmitted in basic units called packets.Each packet is divided up into multiple segments each serving a specialfunction in the data transmission process. A standard packet contains apreamble, a header, a control segment, a data segment, and an SFTsegment, as shown in FIG. 6. Some of the more commonly used codingpatterns for the data segment as shown in FIG. 7 are listed hereunder:

[0008] Non return to zero (NRL)-L coding: according to this technique, ahigh bit “1” in the data is represented by positive voltage (+V),whereas a low bit “0” is represented by negative voltage (−V).

[0009] NRZ-M coding: according to this technique, only when the bitvalue in a continuous bit stream changes from “0” to “1”, the voltage ofthe output signal is changed from the positive voltage (+V) to negativevoltage (−V), whilst the voltage remains in the positive (+V) for allother bit conditions.

[0010] Unipolar return to zero (RZ): according to this technique, forevery high bit “1” in the bit stream the output signal experiences onetransition from negative voltage to positive voltage, and the voltagefor low bit “0” is at the negative.

[0011] Manchester: according to this encoding and decoding technique,the signal changes once in each time unit regardless of the status ofthe data bit. The rising edge of the signal represents a high bit “0”,whilst the falling edge represents a low bit “1”.

[0012] Delay modulation: according to this technique, the voltage of theoutput signal experiences one transition in a time unit for theoccurrence of each high bit “1” in the bit stream, by delaying thevoltage transition from the preceding bit for one time unit beforechanging the voltage. For a low bit “0”, the voltage of the outputsignal is unchanged from the previous time unit, and for two successivelow bits “0”, the signal voltage for the second low bit “0” is theinverse of the voltage for the previous bit.

[0013] In actual operation using the first three signal codingtechniques the signal output does not necessarily experience voltagechange in each time unit, making it more difficult to maintain signalsynchronization at both ends. These techniques thereby are seldomemployed in synchronous communication. The Manchester coding having thecharacteristics of voltage transition in each time unit naturally isbetter for synchronous transmission with wireless means. However, in theManchester coding every bit of information is assigned the same lengthof time, that means a fixed length code is used in the transmissiondata. The difference in transmission time between a variable length codeand a fixed length code is cumulative for larger amounts of transmissiondata, resulting in much longer transmission time than that usingvariable length codes.

[0014] For example, as shown in FIG. 8, using the Manchester codingtechnique, the bit stream 01100011_(—)01011110 represents two data bytes(2 bytes=16 bits). The encoded signals at the transmitting end show thatevery bit in these two bytes is occupied by the same number of timeunits (2T in this embodiment), thus the total transmission time forthese two bytes is 16×2T=32T. Longer transmission time using theManchester coding also consumes more electric power in the datacommunication process.

[0015] The present invention is to address the above mentioned problemwith variable length codes.

SUMMARY OF THE INVENTION

[0016] The main object of the present invention is to provide wirelesscommunication encoding and decoding techniques using variable lengthcodes, wherein a low bit “0” and a high bit “1” in the data stream aredifferentiated by different transmission time, thus enabling reductionin the total transmission time and power saving by the datacommunication device.

[0017] The second object of the invention is to provide wirelesscommunication encoding and decoding techniques using variable lengthcodes, wherein every bit of transmitted data is accompanied by a voltagetransition in the output signal, and the signal synchronization at bothends of the communication link ensures high reliability in datatransmission.

[0018] The wireless communication encoding and decoding techniques usingthe variable length codes comprise the steps of:

[0019] defining a time unit (T);

[0020] defining the number of time units (N) to be assigned forrepresenting the high bit “1”, for example 2T; and

[0021] defining the number of time units (M) to be assigned forrepresenting the low bit “0”, for example 1T;

[0022] wherein two adjacent data bits are to be represented by differentvoltages in the signal output.

[0023] The features and structure of the present invention will be moreclearly understood when taken in conjunction with the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a signal coding method for high and low bits accordingto the new coding technique proposed by the present invention;

[0025]FIGS. 2A, 2B is a comparison between the conventional Manchestercoding pattern and the new coding pattern proposed by the presentinvention;

[0026]FIGS. 3A, 3B are the new code representation of the bit stream01100011_(—)01011110, code with minimum length (00 h), and code withmaximum length (FFh);

[0027] FIGS. 4A˜C show the decoding method used in cyclical samplingwith noise suppression;

[0028]FIG. 5 shows all the possible codes according to the new codingtechnique;

[0029]FIG. 6 shows the various segments of a data packet;

[0030]FIG. 7 is a comparison for several commonly used coding patterns;

[0031]FIG. 8 shows the bit shifting after transmitting the bit stream“01100011_(—)01011110” using the Manchester coding technique.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0032] The present invention provides a new coding technique byassigning different transmission time units (T) to represent low bit “0”and the high bit “1” respectively. The coding method shown in FIG. 1 ispracticed by one embodiment of the present invention in which a low bit“0” is assigned one time unit (T) of transmission time, whereas a highbit “1” is assigned two time units (2T) of transmission time, and twoadjacent data bits are represented by different voltages, that isvoltage changes either from positive to negative, or vice versa.

[0033]FIG. 2 shows a comparison between the conventional Manchestercoding pattern and the new coding pattern proposed by the presentinvention. The bit stream to be transmitted is “01100011_(—)001011110”,where the low bit “0” is represented by one time unit (T), and the highbit “1” by two time units (2T), and the total transmission time used bythe above bit stream is 25T; however, the transmission time usingManchester coding takes 32T. The difference in transmission time isattributed to the fact that in the Manchester coding every data bitrequires two time units (2T) in transmission, whereas the new codingtechnique only uses one time unit for the low bit and two time units forthe high bit. Therefore the new coding technique proposed by the presentinvention using variable length codes enables reduction in transmissiontime over the long term.

[0034] Referencing FIG. 3, if the transmitted data value is 00 h (thehexadecimal representation for data value “0”), the transmission timecan be finished in 16 T time with the new coding technique. For datavalue FFh (the hexadecimal representation for data value “1”), then thetransmission time used is longest with 32T, which is the same as thetransmission time for conventional signal coding technique. However, theaverage transmission time can be reduced by 25% for a bit streamcontaining unspecified number of low bits and high bits.

[0035] In actual practice, the new coding pattern enables even moreflexibility in the data transmission. For example, a low bit “0” can berepresented by 2T, and a high bit “1” by 1T.

[0036] The decoding operation at the receiving end is based on acyclical sampling technique, which has incorporated a certain tolerancerange for possible discrepancies. As shown in FIG. 4A, if the bit value“0” is defined to be 5 t, and the bit value “1” is to be 10 t, where trepresents a unit of time required for performing a complete samplingcycle, a suitable tolerance value can be set up in defining the dataframe for signal reception. For example, a signal in the range 8 t˜12 trepresents bit value “1”, and a signal in the range of 3 t˜7 t torepresent a bit value “0”. During data reception as shown in FIG. 4B,the data value still can be correctly identified using the new signalcoding technique. If any noise is present in the transmitted data asshown in FIG. 4C, they can be filtered out from the incoming signalsbecause noise only remains for one time unit (t) or less.

[0037]FIG. 5 shows all the possible codes according to the new signalcoding technique, wherein different transmission times are assigned forbit values “0” and “1”, and by further incorporation of differentvoltage levels, a code table can be created to include all unique datapatterns. There are a total of nine coding patterns as shown in FIG. 5to represent nine different types of data streams.

[0038] The new signal coding technique is more advantageous in that:

[0039] (1) Reduction of total transmission time: by using a codingscheme with different time units to represent bit values “0” and “1”respectively;

[0040] (2) Power saving: the power for the data communication device canbe saved in proportion to the reduction in transmission time;

[0041] (3) Trouble-free signal synchronization: simple synchronizationfor the transmitting and receiving ends, thus leading to improvedstability and reliability in data transmission.

[0042] The foregoing description of the preferred embodiments of thepresent invention is intended to be illustrative only and, under nocircumstances, should the scope of the present invention be sorestricted.

What is claimed is:
 1. A wireless communication encoding technique usingvariable length codes, comprising: defining a transmission time unit interms of (T); defining a bit “1” using N time units to be (N×T);defining a bit “0” using M time units to be (M×T); wherein the values ofM and N are not to be equal, and two adjacent data bits are representedby different voltages in output signal.
 2. The wireless communicationencoding technique using variable length codes as claimed in claim 1,wherein the time value N is to be greater than M.
 3. The wirelesscommunication encoding technique using variable length codes as claimedin claim 1, wherein the time value N is to be less than M.
 4. A wirelesscommunication decoding technique using variable length codes,comprising: defining a basic time unit in terms of (T); defining bit “0”using N time units to be (N×T); defining bit “1” using M time units tobe (M×T), wherein the values of M and N are not to be equal.
 5. Thewireless communication decoding technique using variable length codes asclaimed in claim 4, wherein the time value N is to be greater than M. 6.The wireless communication decoding technique using variable lengthcodes as claimed in claim 4, wherein the time value N is to be less thanM.